Elliott Digger Derrick - Elongation; Dynamic (Shock) Loading

Synthetic Rope Usage EEC-0060 V1.2
Synthetic Rope Usage,
Inspection, and Retirement
Elongation
It is well accepted that ropes with lower elongation under load will give you better
load control-a big help at complicated job sites. However, ropes with lower elongation
that are dynamic loaded, like a towering line, can fail without warning, even though it
appears to be in good shape. Low elongating ropes should be selected with the highest
possible strength. Both twisted ropes and braided ropes are suitable for rigging. Twisted
rope has lower strength and more stretch. Braided rope has higher strength and lower
stretch.
Dynamic (Shock) Loading
Working loads as described herein are not applicable when rope has been
subjected to dynamic loading. Whenever a load is picked up, stopped, moved, or swung
there is an increased force caused by the dynamic nature of the movement. The force
increases as these actions occur more rapidly or suddenly, which is known as dynamic,
or shock, loading.
An example of applications where dynamic loading occurs includes ropes used
as a tow line, picking up a load on a slack line, or using rope to stop a falling object. In
extreme cases, the force put on the rope may be two, three, or more times the normal
load involved. Dynamic-loading effects are greater on a low elongation rope such as
polyester than on a high-elongation rope such as nylon, and greater on a short rope
than on a long one.
For example, the dynamic load on a winch line that occurs when a 5,000-lb
object is lifted vertically with a sudden jerk can weigh 30,000 lbs. under the dynamic
force. If the winch line is rated in the 30,000-lb break strength range, it is very likely to
break.
Where dynamic loads, sustained loads, or where life, limb or valuable property is
involved, it is recommended that an increased working load factor be used. It is also
recommended that a lower working load factor be selected with only expert knowledge
of conditions and professional estimates of risk; if the rope has been inspected and